The present invention relates to a substrate for a mirror for EUV lithography comprising a main body and a polishing layer, and to a mirror for an EUV projection exposure apparatus, comprising such a substrate and a highly reflective layer on the polishing layer.
In order to be able to produce ever finer structures during the production of, for example, semiconductor components by lithographic methods, light having ever shorter wavelengths is employed. If light in the extreme ultraviolet (EUV) wavelength range is employed, for instance at wavelengths of between approximately 5 nm and 20 nm, it is no longer possible to employ lens-like elements in transmission, rather illumination and projection lenses are constructed from mirror elements having highly reflective coatings adapted to the respective operating wavelength. In contrast to mirrors in the visible and ultraviolet wavelength ranges, even theoretically only maximum reflectivities of less than 80% can be achieved per mirror. Since EUV projective devices generally have a plurality of mirrors, it is necessary for each of these to have the highest possible reflectivity in order to ensure a sufficiently high total reflectivity.